Two Holt 45 gas crawling-type ("caterpillar") tractors team up to pull a long wagon train in the Mojave Desert during construction of the Los Angeles Aqueduct in 1909.
The Origins of the Caterpillar Name (Source: Wikipedia)
The steam tractors of the 1890s and early 1900s were extremely heavy, sometimes weighing 1,000 pounds (450 kg) per horsepower, and often sank into the rich, soft earth of the San Joaquin Valley Delta farmland surrounding Stockton, California. Benjamin Holt attempted to fix the problem by increasing the size and width of the wheels up to 7.5 feet (2.3 m) tall and 6 feet (1.8 m) wide, producing a tractor 46 feet (14 m) wide. But this also made the tractors increasingly complex, expensive and difficult to maintain.
Another solution considered was to lay a temporary plank road ahead of the steam tractor, but this was time-consuming, expensive, and interfered with earthmoving. Holt thought of wrapping the planks around the wheels. He replaced the wheels on a 40 horsepower (30 kW) Holt steamer, No. 77, with a set of wooden tracks bolted to chains. On Thanksgiving Day, November 24, 1904, he successfully tested the updated machine plowing the soggy delta land of Roberts Island.
Company photographer Charles Clements was reported to have observed that the tractor crawled like a caterpillar, and Holt seized on the metaphor. "Caterpillar it is. That’s the name for it!" Some sources, though, attribute this name to British soldiers in July 1907. Two years later Holt sold his first steam-powered tractor crawlers for US$5,500, about US$128,000 today. Each side featured a track frame measured 30 inches (760 mm) high by 42 inches (1,100 mm) wide and were 9 feet (2.7 m) long. The tracks were 3 inches (76 mm) by 4 inches (100 mm) redwood slats.
Holt received the first patent for a practical continuous track for use with a tractor on December 7, 1907 for his improved "Traction Engine" ("improvement in vehicles, and especially of the traction engine class; and included endless traveling platform supports upon which the engine is carried").
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